Hi, Is still the latest version in Debian https://packages.debian.org/stretch/tor what should we do to update it?

Current Debian stable (10, Buster) ships tor version 0.3.5.8 (supported until Feb 1, 2022) if you are on 0.2.9.x you run Debian oldstable. So one option would be to upgrade to Debian stable (Buster) if there are no specific reasons to stay on Debian oldstable.

You can also use the Tor Project's debian repositories if you want to run the latest stable release 0.4.2.5

https://2019.www.torproject.org/docs/debian.html.en